This study investigates the coordination behaviour of potentially bi- and tridentate O,O- and O,N,O-donor Schiff base ligands with trivalent lanthanide ions. The reactions of lanthanide nitrates with 2-((E)-(tert-butylimino)methyl)-6-methoxyphenol (HL1) have yielded five complexes that are described by the general formula [Ln(HL1)2(NO3)3] (Ln = Ce, Nd, Gd, Ho and Er) and were characterised using physico-chemical techniques including single-crystal X-ray diffraction spectroscopy. The cerium complex crystallised in a triclinic (P-1) space group, while the rest of the complexes crystallised in the monoclinic (P21/c) space group. All the complexes are ten-coordinate adopting a tetradecahedron geometry with two HL1 molecules coordinated through the phenolic and methoxy oxygen atoms. The coordination sphere is completed by six oxygen atoms from three bidentately coordinated nitrate ligands. Electronic data reveals that only the neodymium, holmium and erbium complexes exhibit weak f-f transitions in the visible region. The redox behaviour of the complexes was also investigated and reported. Five novel complexes were prepared by reacting 2-((E)-(tert-butylimino)methyl)phenol (HL2) with [Ln(NO3)3∙xH2O] (Ln = Gd and Dy ; x = 5 or 6) and [LnCl3∙6H2O] (Ln = Nd, Gd and Dy). The crystal structures of the former two complexes are isostructural and the coordination sphere is composed of three HL2 ligands bonded to the metal centre through the phenolic oxygen atom and three nitrate ions coordinated in a bidentate fashion. Both complexes are nine-coordinate and SHAPE analysis reveals that they adopted a muffin geometry. The average Ln-Onitrate and Ln-Ophenolate bond lengths are 2.5078 and 2.2814 Å, respectively. The complexes derived from the chloride salts exhibited an octahedral geometry with four monodentate ligands [Ln-Ophenolate distances range from 2.224(4) to 2.2797(17) Å] coordinating in the equatorial positions and two chloride ions [average Ln-Cl bond length is 2.6527 Å, and average Cl-Ln-Cl angles is 180o] in axial positions. The ligand coordinated through the phenolic oxygen with the phenolic proton migrating to the imino nitrogen to give a zwitterionic form of the ligand. There are weak C-H∙∙∙Cl interactions present and O-H∙∙∙N hydrogen bonds are also observed in the crystal packing. The synthesis of lanthanide complexes with methoxy-6-((E)-(phenylimino)methyl)phenol (HL3) was carried out in methanol to yield two mononuclear complexes with the formulae [Nd(HL3)2(NO3)3] and [Ho(HL3)(NO3)3(DMF)(H2O)]. Single-crystal crystallographic studies shows that the neodymium complex contains two HL3 ligands coordinated bidentately through its methoxide and phenolic oxygen atoms, with three nitrate ions also bonded to the metal in a bidentate manner. The coordination geometry in the holmium complex is composed of only oxygen atoms from the various ligands. Both complexes are ten-coordinate and exhibit a tetradecahedron geometry.
| Identifer | oai:union.ndltd.org:netd.ac.za/oai:union.ndltd.org:nmmu/vital:27016 |
| Date | January 2017 |
| Creators | Mkwakwi, Kwakhanya |
| Publisher | Nelson Mandela Metropolitan University, Faculty of Science |
| Source Sets | South African National ETD Portal |
| Language | English |
| Detected Language | English |
| Type | Thesis, Masters, MTech |
| Format | vi, 134 leaves, pdf |
| Rights | Nelson Mandela Metropolitan University |
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